Ignition device having elongated planar parallel electrodes between which a pulse of ionizable gas is passed



July 21, 1970 3,521,105

IGNITION DEVICE HAVING ENLONGATED PLANER PARALLEL ELECTRODES H. E. FRANKS BETWEEN WHICH A PULSE OF IONIZABLE GAS IS PASSED Filed Sept. 25. 1967 3 Sheets-Sheet l v FIG.2

//W/VTO/?= HARRY E. FRAN Ks. I

IBLmR BvckLts cam -Q G ATTORNEYS 1 July 21, 1970 H. E. FRANKS 3,521,105

, IGNITION DEVICE HAVING ENLONGA'I'ED PLANER PARALLEL ELECTRODES BETWEEN WHICH A PULSE OF IONIZABLE GAS IS PASSED Filed Sept. 25, 1967 3 Sheets-Sheet 2 '//v|//vmq HARRY E. FRANKS bunk Bvuurs Lawn ST-ousE ATTORNEYS H. E. FRANKS 3,521,105

3 Sheets-Sheet 3 July 21, 1970 IGNITION DEVICE HAVING ENLONGATED PLANER PARALLEL ELECTRODES BETWEEN WHICH A PULSE 0F IONIZABLE GAS IS PASSED Filed Sept. 25, 1967 United States Patent US. Cl. 313120 3 Claims ABSTRACT OF THE DISCLOSURE An improved spark plug has a pair of spaced, planar, substantially parallel, opposing electrodes of substantial surface area. An auxiliary electrode located between the first pair of electrodes can be utilized to initiate a spark between them.

In another version of the invention a spark-generated plasma is injected into the combustion chamber of an internal combustion engine to ignite the charge in the chamber.

BACKGROUND OF THE INVENTION Field of the invention This application is a continuation-in-part of application Ser. No. 649,232, filed June 27, 1967.

Spark plugs are devices which provide a high energy spark between a pair of spaced electrodes. They are utilized most frequently in internal combustion engines to provide an igniting spark for the fuel supplied to the cylinders of the engine, but they also have many other uses such as in triggering pumping lamps for solid state pulsed lasers.

Prior art In spark plugs of the type previously known, a pair of parallel, spaced electrodes of relatively small dimensions and relatively small mass are positioned opposite each other to define a spark gap between the opposing faces. These electrodes are held in place "by means of an insulating body to which they are attached. The insulating body not only supports the electrodes, but also insulates them from each other so that a relatively large potential difference can be built up across the electrodes when desired without premature firing.

During the course of repeated electrical discharges, the opposed faces of the electrodes become increasingly pitted. This pitting increases the effective path length between the electrodes and therefore increases the potential needed for discharge. Ultimately, it causes "weak sparks and even failure to spark when required. The problem is particularly serious in internal combustion engines, in which the spark plugs must be regularly replaced for satisfactory performance.

In applications which require a high-energy discharge between the electrodes, the electrodes are positioned a substantial distance apart. A relatively high starting voltage is thus required to initiate a discharge between the electrodes, this voltage being substantially larger than that required to maintain the discharge once it is established. This requirement imposes onerous restrictions on the spark plug power supply.

SUMMARY OF THE INVENTION Accordingly, it is an object of my invention to provide an improved spark plug. Another object of my invention is to provide an improved spark plug having an extended lifetime and in which the causes and effects of pitting are minimized. A further object of my invention is to provide an improved spark plug in which the deterioration in the power in the sparks is substantially reduced. Still a further object of my invention is to provide an improved spark plug of the type which utilizes an additional electrode to control the firing potential of the spark.

Another object of the invention is to provide improved ignition of the charge in the combustion chamber of an internal combustion engine.

In accordance with my invention, I provide a spark plug having a pair of spaced, planar, substantially parallel opposing electrodes of large active surface area to re 'duce the effects of pitting. Should pitting occur, however,

the increase in the current path length between the pitted portion of the electrode surface and the opposite electrode causes the spark to shift to other portions of the electrodes which are not pitted and which thus provide a shorter current path length between them. With the greatly enlarged surface area of my spark plugs, this skipping action can proceed for a long time before the pitting significantly increases the path length over the entire electrode structure.

In applications in which the spark plug is only inter-- mittently operated, the electrodes may be provided withv substantial thermal mass to prevent excessive heating of their active surfaces. This also minimizes pitting.

In one embodiment of my invention, an auxiliary electrode is interposed between the main electrodes and forms a secondary spark gap with one of them. Firing of the secondary spark gap ionizes the air in the vicinity of the main electrodes and causes them to fire at a lower potential than they otherwise would. This configuration is especially useful in triggering the pumping lamp in a solid state pulsed laser.

In another embodiment of the invention, the spark plugs are used to generate hot plasma jets which are injected into the combustion chambers of an internal combustion engine to initiate combustion therein.

The invention accordingly comprises the apparatus embodying features of construction, combinations of elements and arrangement of parts which are adapted to effect such steps, all as exemplified in the following detailed disclosure, and the scope of the invention will be indicated in the claims.

The above and other further objetcs and advantages of my invention will be more readily understood when taken in connection with the following detailed description of the drawings, in which:

FIG. 1 is an elevational view, in section, of a preferred form of spark plug constructed in accordance with my invention;

FIG. 2 is a plan view along the lines 22 of FIG. 1;

FIG. 3 is a sectional view of another embodiment of my invention in which one of the electrodes is formed integral with the housing;

FIG. 4 is an elevational view, in section, of a spark plug constructed in accordance with my invention and which is particularly suitable for use in internal combustion engines;

FIG. 5 is an end view of the spark plug of FIG. 4;

FIG. 6 is an elevational view, in section, of yet another spark plug constructed in accordance with my invention and shown positioned within a cylinder of an internal combustion engine; and

FIG. 7 is a sectional view along the lines 77 of FIG. 6.

SPECIFIC DESCRIPTION In FIGS. 1 and 2 of the drawings, a spark plug 10 constructed in accordance with my invention comprises a pair of main electrodes 12, 14 which are attached to supporting plates 16, 18, respectively. The electrodes are formed with external threads which mate with corresponding threads in the plates 16 and 18; slots 13 in the electrodes provide for screw driver adjustment of their axial positions to provide the desired inter-electrode gaps. The electrodes are formed from materials having high electrical and thermal conductivity, such as aluminum, although other materials such as stainless steel and Monel metal, a trademark for a nickel base alloy containing approximately 68% nickel, 29% copper, and 3% iron, manganese, silicon, and carbon, have advantageously been used. The plates 16 and 18 may be formed either from nonconductive materials such as insulating ceramics r epoxies or from conductive materials such as metals; in the latter case, recessed areas 20, 22 are formed around the electrodes 12 and 14, respectively, in order to increase the path length from a given electrode to the opposite supporting plate.

A hollow insulator 24 extends between the plates 16 and 18 on the left side of the spark plug; similarly, a pair of hollow insulators 26 and 28 extend between the plates 16 and 18 on the right-hand side of the spark plug. The latter insulators support an auxiliary electrode 36 which is positioned between them. Insulating bolts 30 of nylon or other nonconductive material extend through the supporting plates 16 and 18, the insulators 24, 26 and 28, and through an aperture 40 in the electrode 36; nuts 32 are threaded onto the ends of the bolts to secure the component parts of the spark plug tog-ether.

A central aperture 38 extends through the auxiliary electrode 36 in line with the opposed surfaces of the electrodes 12 and 14. Effectively, the electrode 36 shields the electrodes 12 and 14 from each other everywhere except in the vicinity of the aperture 38; in this area, a main spark gap is formed between the opposing, active surfaces of the electrodes 12 and 14 in a relatively straight line through the aperture 38. An auxiliary spark gap is formed between the electrode 36 and one of the electrodes 12 and 14.

Leads 42, 44 and 46 connect each of the electrodes 12, 14 and 36, respectively to a power supply 48. The power supply has a push button switch 50 for establishing an electrical potential difference between the electrode 36 and a main electrode 12 or 14 to initiate a starting spark between the appropriate electrodes.

In a typical application of the spark plug shown in FIGS. 1 and 2, electrodes 12 and 14 of one-inch diameter were used in conjunction with a one-half inch aperture 38 to excite a laser head. The auxiliary gap was .015 inch and the main gap was .035 inch; the electrode 36 was a few thousandths of an inch thick. A potential difference of 10,000 volts was applied across the auxiliary gap and thus ionize the air in the vicinity of the spark. When this was done, a 4,000-volt potential difference between the main electrodes 12 and 1-4 was sufficient to sustain a spark between them. Thus the use of an auxiliary electrode in the spark plug limits the requirements imposed on the main electrode power supply.

It will be observed that the areas of the surfaces of the electrodes 12 and 14 between which the spark gap forms (the active surfaces) are substantially larger than the corresponding electrode areas of spark plugs heretofore utilized. For the example of my invention in which the electrodes 12 and 14 have a diameter of one inch, the active electrode area of each is equal to 7r/4 square inches. As a result of this increased area, a much larger number of separate current paths between the two electrodes may be established. Thus, should the surface of either of the electrodes 12, 14 become pitted at any particular point, the increased current path length between the pitted area and the surface of the opposite electrode causes the current to follow an alternate path and thus prevents further pitting at that point.

In contrast, in spark plugs of the type known to the prior art, the limited surface area of the electrodes minimizes the number of alternate current paths and thus pitting proceeds to ultimate destruction of the electrodes more rapidly.

Further, in applications such as the pumping of laser heads in which the spark plug is operated intermittently, the large thermal mass of the electrodes assists in maintaining a low surface temperature. This further reduces the tendency of the electrodes to pit.

As a specific example of the advantageous results obtainable, a spark plug constructed in accordance with my invention and having an active area of 1r/4 square inches (corresponding to a diameter of one inch) was pulsed with a one-thousand ampere current at a pulse repetition rate of ten pulses per second for over one million pulses (about twenty-eight hours of operation) without appreciable deterioration and with no substantial change in the gap length. In contrast, a conventional spark plug operating under the same conditions pitted to such an extent that it was substantially unusable after ten thousand pulses (about seventeen minutes of operation). At lower currents, the lifetime of my spark plug would be prolonged indefinitely.

FIG. 3 is an elevational view, in section, of an alternative embodiment of my invention in which the auxiliary electrode is omitted. As shown in the drawing, upper and lower housing elements 62 and 64 are electrically insulated from each other by an insulating spacer 66. The upper housing element 62 has a central threaded aperture which accommodates a threaded electrode 68 whose position in the aperture may be adjusted by means of a slot 69 in the electrode. An electrode 70 is integral with the lower housing element 64. Electrical leads 72 and 74 are attached to the upper and lower electrodes respectively; these leads are connected to an appropriate power supply (not shown).

The structure of FIG. 3 advantageously lends itself to rather simple mass production techniques resulting in both economy and simplicity of construction. The heat dissipating capabilities of the electrode 70 are further increased by the unitary construction. Of course, an auxiliary electrode may be utilized in this structure if desired.

So far I have described my invention with respect to spark plugs of the type suitable for use in triggering the pumping lamp in a solid state laser head. My invention is not so limited, however, and is especially useful for supplying the igniting spark in internal combustion engines; indeed, this may well be its primary use. FIG. 4 shows one embodiment particularly suitable for this use. A terminal 84 formed from an electrically conductive material is seated in an insulating body 82 formed of nonconductive material such as insulating ceramic. The terminal 84 is attached to a solid bar conductor '86 which extends longitudinally through the body and which is attached at its lower end to an electrode 88 of generally circular configuration; the electrode has one portion cut away as shown in FIG. 5. An electrode 90 is positioned opposite the electrode 88 in spaced, opposing relation to define a spark gap between the two electrodes. The electrode 90 is electrically connected via an electrically conductive bar 92 to a threaded mounting shank 94. The shank 94, which is also formed from electrically conductive material, mounts the spark plug in the internal combustion engine in the usual manner and serves as a grounding terminal for the electrode 90.

Although the spark plug shown in FIGS. 4 and 5 resembles conventional spark plugs in many respects, its uniqueness will immediately be apparent on consideration of the electrodes 88 and 90. Each of these electrodes has a substantial active surface area and therefore they provide a larger number of alternating current paths between them than do electrodes of the conventional type in which the limited electrode area causes an earlier ultimate destruction of the electrodes.

Although the specific dimensions of the electrodes may be varied to suit the needs of the user, their active surface area should be as large as possible to maximize the lifetime of the spark plug. Thus, the area of each face should be at least as large as .0 3 square inch (about ten times the active surface area of the smaller electrode of plugs now in existence) and is preferably substantially larger. Where the spark plug is to be inserted into an automobile engine, for example, the lateral and longitudinal dimensions of the electrodes should be limited only by the bore through which the plug is inserted into the engine block; in such a case, the lifetime of the electrodes may well extend beyond that of the rest of the engine.

FIGS. 6 and 7 depict another spark plug for internal combustion engines. A spark plug 100 has an electrically insulating body 102 of nonconductive ceramic or other material and a terminal head 104 for attachment to a source of electrical potential. The head 104 is connected to a conductor 106 extending longitudinally through the body of the spark plug and forming a first spark electrode. A second spark electrode 108 is positioned within the body 102 in spaced, opposing relation to the electrode 106. The electrode 108 is connected to a conventional threaded, electrically conductive mounting shank 110 to mount the spark plug 100 in a cylinder 112 of an engine block 114.

The electrodes 106 and 108 extend a substantial distance along the length of the spark plug body. As is the case with prior embodiments of my invention, these electrodes have a substantial active surface area and thus possess an extended lifetime, with respect to pitting as discussed above in connection with prior figures of the drawings. The plane of the opposing face of one of the electrodes is positioned at a very slight angle (on the order of 1 or 2 degrees) to the plane of the opposing face of the other electrode, so that the spark gap between the electrodes is narrowest at the bottom and pro gressively increases toward the top. This ensures that the spark will form at the lower portion of the electrodes when the spark plug is first put in use and will only gradually Work its way up the electrodes as wear occurs. In practice, with currents and duty cycles of the order now used in conventional automobile engines, the spark will probably travel up the electrodes no further than approximately one-quarter inch.

An inlet port 115 is located in the upper portion of the spark plug to carry the gasoline or other fuel to be burned from an external source (not shown) to the interior of the plug between the spark electrodes 106 and 108 and into the cylinder 112. This assists in clearing the spark gap of residual combustion products which may accumulate in the spark gap in cases where the operation of the plug is continued after the spark has advanced up the electrodes. In most cases, however, this advance of the spark should be quite limited; in such cases, the channel 115 may be omitted and fuel may be supplied to the cylinder 112 by conventional techniques.

In another version of the invention, the fuel is admitted to the cylinder 112 of FIG. 6 through the usual intake valve or fuel injection nozzle used in present day engines. A pulse of air or inert gas is then fed to the port 115 in synchronism with the spark between the electrodes 106 and 108. The spark heats and ionizes the gaseous stream between the electrodes So that a palsma jet issues from the electrode gap. This hot jet readily ignites the charge in the cylinder.

More specifically, the plasma jet will ignite charges that are too lean for reliable ignition by a spark. Furthermore, it will provide more complete combustion of the charge. The resulting advantages, in terms of increased efiiciency and diminished air pollution from incompletely combusted hydrocarbons, will be obvious.

The gaseous pulses may be applied to the spark plug ports in an engine through camor solenoid-operated valves connected between the ports and a high pressure source of the gas (e.g. a conventional bottle). The valves may be actuated by cams on the distributor rotor shaft, or suitable magnetic sensors around the shaft may be used to energize solenoids operating the valves. Each valve will usually be timed to open for a short interval beginning just prior to the spark in the spark plug connected to the valve. It will be understood that the temperature, intensity and duration of the jet are kept below the levels at which they will damage the cylinder walls, piston, etc., of the engine.

From the above it will be seen that I have provided an improved spark plug having a pair of opposed, planar, substantially parallel electrodes of large active surface area and extended life. Further, I have provided a spark plug having an auxiliary electrode for initiating a spark across the gap between the main electrodes when these are positioned a substantial distance apart.

Having illustrated and described a preferred embodiment of my invention, what I claim as new and desire to secure by Letters Patent is:

1. An ignition device comprising an insulator body, means, associated with said insulator body, for mounting said device, a first substantially planar electrode, supported by the said insulator body, extending longitudinally in said device, a second substantially planar electrode, supported in spaced, facing relationship relative to said first electrode by said insulator body, extending longitudinally in said device, said space constituting a spark gap along the longitudinal extent of said electrodes, inlet means for accessing through said device the ignition area served by said device including the passage formed by said space between said electrodes and means for interconnecting said space with the outer surface of said device, and a source of plasma gas interconnected with said inlet means.

2. The device of claim 1 in which said electrodes are divergent having their ends communicating with the ignition area closer together than their other ends.

3. The device of claim 1 in which said ignition device further includes means for projecting a pulse of gas through said space between said electrodes simultaneously with a spark discharge between said electrodes.

References Cited UNITED STATES PATENTS 1,596,240 8/1926 Dikeman 3 13-120 X 3,088,282 5/1963 Logan 3l3l3l-X 3,219,866 11/1965 Dingman 313l18 3,330,985 7/1967 Johnston 31323l X 3,356,897 12/1967 Barr et al. 313-231 X JAMES W. LAWRENCE, Primary Examiner E. R. LA ROCHE, Assistant Examiner US. Cl. X.R. 313-128, 141, 231 

